A Quasi-Coherent Electrostatic Mode in ECRH Plasmas on TJ-II

Abstract

A new type of instability mode, related to suprathermal electrons, was found in extremely low-density plasmas, (n e = (0.2-0.5) × 10 19 m −3 ) with electron cyclotron resonance heating and current drive (ECRH/ECCD) in the TJ-II heliac. The quasi-monochromatic density and plasma potential oscillations in the frequency range 20-120 kHz tend to have several "branches" with constant frequency shift between them. The typical amplitude of the mode induced potential oscillations was estimated to be Δϕ EM ∼ 20 V. The mode branches have an individual and finite radial extent, odd low poloidal structure (m ≤ 5) and angular phase velocity of poloidal rotation of about 8 × 10 4 rad/s in the ion diamagnetic drift direction. The contribution of the mode to the turbulent particle flux Γ E×B for the observed wave vectors k θ < 3 cm −1 was found to be small in comparison with the contribution from broadband turbulence.

Experimental characterization of a quasi-coherent turbulent structure in the edge plasma in Wendelstein 7-X

“…For instance, the electromagnetic mode at f mode ≈ 26.5 kHz observed in the pedestal region of EAST tokamak is responsible for an outward particle transport in the low wavenumber range (k ⊥ < 3 cm −1 ) [14]. Also in the TJ-II stellarator a quasi-coherent electrostatic mode at f = 20 ∼ 120 kHz was observed to contribute to a small fraction of the turbulent particle flux for k θ < 3 cm −1 [15]. From the modeling point of view, the coupling between ion drift waves and electron drift-acoustic waves implies an important destabilization effect for a driftballooning mode, which might be related to the quasi-coherent edge instabilities at the H-mode pedestal [16].…”

50 Years of Hot Plasma Diagnostic With Heavy Ion Beam Probing (Hibp) at the Kharkov Institute of Physics and Technology

“…The new type of quasicoherent modes were discovered on TJ-II using HIBP. These are oscillations excited by fast (supra-thermal) electrons (ST-mode) and resonant oscillations of plasma density [81,82].…”

Contribution to fusion research from IAEA coordinated research projects and joint experiments

“…An elevated non-Maxwellian tail into the plate results in an overestimate of the temperature estimation by divertor Langmuir probes by a factor of 2-6, using classical probe techniques [10,14].…”

“…The induced modes, AEs are driven by the energy transfer from energetic ions to the waves. Energetic electrons may also excite quasi-coherent modes under some conditions [14,15].…”